1. Field of the Invention
This invention pertains to the field of resin systems including curable thermoset resins, composite materials and skin laminates for composite materials, and processes for making the same.
2. Description of Related Art
Known gel coated fiber-reinforced polymers are subject to blistering if immersed in water or solvents for a prolonged period of time unless special measures are taken to prevent this phenomenon. Blisters are raised by localized swelling of the gel coated laminate due to diffusion of water into the composite and the presence of water-soluble constituents within the laminate. The blisters not only effect the external appearance of the gel coated fiber-reinforced polymer article, but also eventually lead to reduced composite strength.
Several methods have been proposed to reduce blistering in gel coated composite materials. U.S. Pat. No. 4,724,173 describes using a permeable gel coat to allow the osmotically active molecules to diffuse from the osmotic centers through the gel coat at a defined transport rate whereby the osmotic pressure of the osmotic centers is reduced so as to reduce blistering. U.S. Pat. No. 4,477,325 describes a method of manufacturing a skin barrier which has improved water resistance to protect the composite material from hydrolysis. U.S. Pat. Nos. 4,480,077 and 4,525,544 describe vinyl ester resin compositions which may be used in the laminate construction to impart greater resistance to water permeation and U.S. Pat. No. 4,959,259 describes a bisphenolic polyester resin composition which may also be used to impart greater water permeation resistance.
The latter technique, using a laminate resin having greater corrosion and/or water resistance, is the most common technique used by the composite industry to reduce blistering. Those resins are typically vinyl ester resins or isophthalic polyester resins. Not only is that technique not always completely successful, it also increases the overall expense of the composite material and/or reduces the flexibility in choosing the laminating resin for other desired properties.
For these and other reasons, further improvements in the ability to prevent blistering are desired. These and other objectives are achieved by the present invention.
One aspect of this invention is curable thermoset resin compositions useful for imparting water and/or solvent resistance to gel coated fiber-reinforced polymers comprising:
(A) At least 5 wt. % of an at least partially end-capped unsaturated polyetherester resin;
(B) An unsaturated polyester resin having a ratio of the number average molecular weight to the average number of double bonds per polymer molecule in the range from about 200 to about 400, in an amount such that the weight ratio of polyester resin (B) to polyetherester resin (A) is in the range from about 10:90 to about 90:10;
(C) About 10 to about 70 wt. % of at least one vinyl monomer; and
(D) A curing agent.
Another aspect for this invention is a method for making a curable thermoset resin compositions comprising combining:
(A). At least 5 wt. % of an at least partially end-capped unsaturated polyetherester resin;
(B) An unsaturated polyester resin having a ratio of the number average molecular weight to the average number of double bonds per polymer molecule in the range from about 200 to about 400, in an amount such that the weight ratio of polyester resin (B) to polyetherester resin (A) is in the range from about 10:90 to about 90:10;
(C) About 10 to about 70 wt. % of at least one vinyl monomer; and
(D) A curing agent.
A further aspect of this invention is an intermediate for making a curable thermoset resin composition comprising
(A) At least 5 wt. % of an at least partially end-capped unsaturated polyetherester resin;
(B) An unsaturated polyester resin having a ratio of the number average molecular weight to the average number of double bonds per polymer molecule in the range from about 200 to about 400, in an amount such that the weight ratio of polyester resin (B) to polyetherester resin (A) is in the range from about 10:90 to about 90:10; and
(C) About 20 to about 50 wt. % of at least one vinyl monomer.
Definitions
The term xe2x80x9cend-capping compoundxe2x80x9d as used herein means a compound having at least one functional group capable of reacting with at least one reactive end group of the unsaturated polyetherester resin such that the acid number of the unsaturated polyetherester resin is reduced. When the end-capping compound has more than one functional group per molecule, then the functional groups are selected such that they have, under the same conditions, a greater propensity to react with a reactive end group of the unsaturated polyetherester resin than with another functional group of the end-capping compound to avoid substantial polymerization of the end-capping compound with itself. The functional groups of the end-capping compound are preferably the same, or are known to be substantially unreactive with each other.
The term xe2x80x9ccuringxe2x80x9d and xe2x80x9ccuredxe2x80x9d refer to the formation of a substantially irreversible three-dimensional crosslinking network in a curable polymer composition such that the polymer forms a structure that is substantially insoluble in solvents for the uncrosslinked polymer.
The term xe2x80x9cbisphenol-Axe2x80x9d refers to 2,2-bis(4-hydroxyphenylpropane).
The term xe2x80x9cunsaturated polyetherester resinxe2x80x9d means polymer resins of intermediate molecular weight that contain ethylenic unsaturation available for free-radical polymerization with a vinyl monomer, recurring ester units, and recurring polyether blocks. The polyether blocks have repeat units of oxyalkylene groups (-O-alkylene-), which in a preferred embodiment have from 2 to 10 carbon atoms each (e.g., oxypropylene, oxyethylene, etc.), more preferably from 2 to 4 carbon atoms. Preferably, the unsaturated polyetherester resins have an ether/ester mole ratio of at least about 0.75, more preferably at least about 1 and preferably not greater than about 3. The number average molecular weight of these resins is preferably in the range from about 500 to about 10,000. They have alcohol and/or carboxylic acid end groups which react with at least one of the end-capping compounds.
Unless otherwise specified herein, the term xe2x80x9cviscosityxe2x80x9d refers to the viscosity of a polymer in styrene monomer at 65 wt. % NVM (non-volatile material, see below) at 25 C. measured using a Brookfield Viscometer.
The term xe2x80x9cNVMxe2x80x9d refers to non-volatile material (a.k.a. xe2x80x9csolidsxe2x80x9d) dispersed in a volatile substance (e.g., styrene monomer) measured according to ASTM D1259.
The term xe2x80x9cASTMxe2x80x9d refers to a well known collection of standard laboratory procedures for measuring the properties of materials published by the American Society for Testing and Materials.
Unless specified otherwise, all ratios, percentages, and parts are by weight.